When loading basic cube as object with some vertex groups as .obj from blender it seems very unpredictable if they will come with vertex groups or not. sometimes one or two,three show, sometimes none.

Is this normal or am i doing something wrong?

I don't think .obj supports vertex groups in the way you're expecting. I believe .obj groups are per face so your "vertex group" in Blender would have to contain enough vertices to define whole faces. I doubt arbitary groups of vertices would translate properly or at all. If you reimport the same .obj back into Blender do you retain all the vert groups exactly how you defined them before exporting? Either way I'd use a more robust file format.